As electrophotographic toners for developing electrostatic latent images formed on the surface of electrophotographic photoreceptors, electrostatic recording media, etc., there have been heretofore proposed many materials. For example, JP-A-54-124731 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses an electrophotographic toner comprising a specified quaternary ammonium polymer. JP-A-59-185353 and 59-187357 disclose a capsule toner comprising a specific quaternary ammonium polymer incorporated in the shell of a capsule. In these toners, anionic components to be contained in the quaternary ammonium polymer are halogens. Further, JP-A-58-120263 discloses an electrophotographic toner comprising a quaternary ammonium group-containing polymer containing as anionic components p-toluenesulfonic acid ion.
However, as a result of studies made by the inventors it has been found that quaternary ammonium group-containing polymers containing as anionic components a halogen ion, a p-toluenesulfonate acid ion or a methylsulfate ion deteriorate the chargeability of toner under high temperature and humidity conditions and thus provide a toner having a poor environmental stability.
In general, processes for producing a polymer containing a quaternary ammonium group comprises quaterizing a corresponding amino group-containing polymer with an alkyl halide (e.g., butyl bromide), benzyl chloride, alkyl p-toluenesulfonate or dimethyl sulfate. However, these processes require a solvent for dissolving or swelling the polymer. This solvent needs to be recovered upon after-treatment. Further, some amino groups need to be processed at a high temperature and a high humidity and thus requires a special apparatus. Moreover, anionic components are limited to halogen ions, a p-toluenesulfonate ion or a methylsulfurate ion.
Other processes for producing a polymer containing a quaternary ammonium group include a process which comprises polymerizing monomers containing a quaternary ammonium group. In accordance with this process, monomers containing anionic components in various forms can be subjected to polymerization. However, it requires much time and labor to prepare monomers containing such anionic components. Some monomers are subject to a change in reactivity which causes a change in the content of quaternary ammonium groups in the polymer resulting in a change in the charged amount of toner particles.
In order to incorporate a quaternary ammonium group in known toners, JP-A-54-124731 and 58-120263 use the former method. JP-A-59-185353 and 59-187357 use the latter method.
Thus, the prior art electrophotographic toners have disadvantages both in their electrophotographic properties and preparation method.